tests/qapi-schema: Cover 'Features:' not followed by descriptions

A 'Features:' line without any features is useless, but not an error
now.  However, a later commit will make it one, because that makes
rejecting duplicate 'Features:' easier.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240216145841.2099240-4-armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

tests/qapi-schema/doc-empty-features.json

@@ -0,0 +1,10 @@
+# 'Features:' line not followed by feature descriptions
+
+##
+# @foo:
+#
+# Features:
+#
+# not a description
+##
+{ 'command': 'foo' }

tests/qapi-schema/doc-empty-features.out

@@ -0,0 +1,19 @@
+module ./builtin
+object q_empty
+enum QType
+    prefix QTYPE
+    member none
+    member qnull
+    member qnum
+    member qstring
+    member qdict
+    member qlist
+    member qbool
+module doc-empty-features.json
+command foo None -> None
+    gen=True success_response=True boxed=False oob=False preconfig=False
+doc symbol=foo
+    body=
+
+    section=None
+not a description

tests/qapi-schema/meson.build

@@ -71,6 +71,7 @@ schemas = [
   'doc-duplicated-return.json',
   'doc-duplicated-since.json',
   'doc-empty-arg.json',
+  'doc-empty-features.json',
   'doc-empty-section.json',
   'doc-empty-symbol.json',
   'doc-good.json',